When I spoke with Tomoyuki Ueyama of OTC DAIHEN at FABTECH® 2015, he was traightforward about the motivation
behind the company’s latest nonpulsed gas metal arc welding (GMAW) technology: It was about
waste reduction.

That shouldn’t come as a surprise to any follower
of lean manufacturing principles. Lean manufacturing has been at the heart of Japanese manufacturing since the late 1970s.

What waste was this welding technology advancement targeting? Ueyama said the desire was to reduce postwelding work needed to remove excessive
spatter and to increase general welding productivity.

The technology behind these potential benefits
is OTC DAIHEN’s new Controlled Bridge Transfer-Expanded (CBT-EX) process. It’s the latest result of
high-speed, high-precision processing made possible by modern inverter-controlled welding power
sources and digitalization.

The company’s Welbee welding power source,
developed in 2010, is the platform on which these
waveforms are being developed. The power source
is equipped with very large-scale integrated circuits
tailored for waveform control and arc stabilization.

The current Welbee control technology allowstechnicians to select certain nonpulsed GMAWUeyama and Tetsuo Era, both owners of severalpatents related to welding technology, came upwith the latest CBT-EX waveform to further build onthe Welbee’s digital power. This latest weld processis actually an improvement of the CBT welding pro-cess. CBT helped to minimize spatter in nonpulsedGMAW, but faster welding speeds were desired. Thefocus was to stabilize the metal transfer in the glob-ular transfer current range.

The method of spatter reduction during rearcing is
similar to the standard CBT process, as seen in
Figure 1. However, the precision processing of the company’s digital power source helps to deliver consistency
in globular transfer mode and improve arc length control during the arc duration. The result is a consistently
sized droplet on the wire tip after each rearc.

More specifically, a high-current pulse is supplied at the beginning of the arcing period, which
increases the wire melting rate and creates a sufficient droplet size at the wire tip. After that, the arc
current, which changes
in real time based on
how metal transfer is
going and the state of
the molten pool, regulates the arc length. This
all contributes to high-speed, low-heat GMAW.

In fact, Era has written
in a position paper that
the process is suitable
for high-speed root pass
pipe welding. (With the
introduction of CO2 as
an assist gas, the process
also might be suitable for
heavy-plate welding, in
which current globular
transfer modes have a
tendency to produce gas
explosions in the molten
pool or droplet explosions caused by overheating associated with
high current.)

Figure 2 shows the CBT-EX process in welding
of a lap fillet joint with 0.06-inch sheet metal using
an argon/CO2 gas mix. This was carried out with a
0.045-in.-diameter solid wire, 200 amps, 18 V, and
a welding speed of 78. 7 inches per minute (IPM).
Company officials report that penetration of more
than 20 percent is possible, and a regular flat bead
has been achieved without any undercut in this application.

Figure 3 shows the new welding process using
100 percent CO2 shielding gas on a lap fillet joint with
a 0.09-in. bottom plate and a 0.06-in. top plate. The
weld was done with a 0.045-in.-dia. wire, 230-amps,
18. 5 V, and a welding speed of 39. 37 IPM. Although
welding was difficult because of the different plate
thicknesses and a 0.04-in. gap, welders involved in
these tests still were able to deposit sufficient metal
to bridge the gap with enough penetration, which
resulted in a regular and flat weld bead.

Ueyama said that although the CBT-EX process
is targeted for robotic applications now, it will be
adapted for manual use in the near future.